1. Field of the Invention
The invention relates to a magnetic head designed notably to form part of a recording and/or reading matrix device.
A magnetic head is a device for the recording and/or reading of information on a magnetic medium, notably a tape. The recording is done by varying the magnetization of the medium locally. This type of magnetic head can be used in magnetic recorders serving for example in computer applications or in on-board equipment or else in video recorders for professional use as well as for large-scale consumer use.
A head such as this has a magnetic circuit with two magnetic poles separated by a non-magnetic gap. For the recording of information elements, a magnetic field is induced in the magnetic circuit and the magnetic medium is placed close to the poles and the gap. Consequently, the magnetic circuit gets closed by the magnetic medium at the position of the gap. This enables the magnetization or demagnetization of the medium at this position.
The reading of information elements recorded on the medium is obtained by an electrical signal that results from an electromotive force induced by the variation of the magnetic flux in the magnetic circuit formed by the medium. This variation of flux arises out of the variation of the magnetization of the medium during a relative shift of the medium and of the head.
2. Description of the Prior Art
In a recording matrix device, it is generally assumed that there is a ratio of 3 between the level of excitation of the address heads and the parasitic signals present in the non-address heads. It is the magnetic medium that provides for the threshold effect discriminating between the levels of write signals and the levels of parasitic signals. In a strong writing field, there appear saturation effects that reduce this ratio of 3. It has been proposed, in the French patent application No. 2 639 137, to place an element, in the gap, made of magnetic material with saturation lower than that of the material of the poles. When the saturable material is not saturated, the magnetic field remains confined in the magnetic circuit and does not go through the medium. When this material is saturated, the magnetic field does not remain confined in the gap. A part of this field goes into the medium and magnetizes it. A recording is done only when the current producing the excitation goes beyond a predetermined threshold.
However, the saturable element introduced into the gap can conduct only a small magnetic flux owing to its size. This material gets saturated swiftly and the writing takes place for low values of excitation. Its effect is almost negligible. This drawback is especially appreciable for matrix devices with narrow tracks. It is not rare for the surface area of the gap perpendicular to the magnetic medium to be in the range of some tens of micrometers square.